In the past, various different types of electronic circuitry have been utilized for controlling the electronic commutation of an ECM, and at least for the most part, such electronic circuitry was in the form of solid state components. Electronic circuitry of the solid state type enabled the versatility of the ECM to be employed in various different types of applications therefor particularly where variable speed and/or variable torque requirements existed. Generally speaking, the electronic circuitry for an ECM comprises a power circuit having solid state switching devices for commutating the power supplied to the ECM to effect its energization, a regulating circuit having various solid state components for maintaining the power supplied to the ECM generally constant, and a control circuit having various solid state components for controlling the conductivity of the switching devices. The disclosures in the various patents enumerated hereinafter are merely representative of the various different approaches employed in the utilization of the ECM and different electronic circuitry therefor as a drive in various different exemplary applications or systems, both of the relatively low power type and high power type.
For instance, in U.S. Pat. No. 4,494,055 assigned to the General Electric Company, a relatively low power application for an ECM driven fan adapted for household use is disclosed having a housing positioned at one end of the ECM and containing the electronic circuitry therefor. In this low power ECM fan drive application, power leads are passed through the ECM into the aforementioned housing at one and thereof to be terminated with the electronic circuitry contained in such housing, and the electronic circuitry is disposed on a printed circuit board secured to such housing. The electronic circuitry includes a regulating circuit, monolithic integrated control circuits which provide drive signals to relatively low power switching transistors of a power circuit. The components of the regulating circuit, the control circuits and the power circuit are all mounted in circuit relation on the aforementioned printed circuit board since the power conducted by the switching transistors is relatively low and, therefore, the heat dissipation from such low power switching transistors is also relatively low being effected through small heat sinks integral with each switching transistor.
In comparison with the above discussed application of the relatively low power ECM and electronic circuitry therefore, the particular applications for the ECM and electronic circuitry therefor of the present invention are of the aforementioned higher power type, and if a more detailed discussion of the construction and operation of such higher power ECM and electronic circuitry therefor is desired, reference may be had to U.S. Pat. Nos. 4,169,990 and 4,556,827 issued to Daniel M. Erdman and U.S. Pat. No. 4,162,435 issued to Floyd H. Wright, all of which are assigned to the General Electric Company. Generally speaking, an ECM has a multi-stage winding assembly and a magnetic assembly associated for relative rotation, and in a given state of energization sequence for the winding stages of the multi-stage winding assembly, the ECM has at least one unenergized winding stage in which an induced back EMF appears. When integrated over time to a predetermined value, the aforementioned induced back EMF indicates the instant at which the relative angular position between the multi-stage winding assembly and the magnetic assembly upon the relative rotation thereof has been attained suitable for the sequential commutation of the next winding stage.
In one example of a past ECM, the magnetic assembly was rotatable with respect to a stationary multi-stage winding assembly, and in another exemplary past ECM, the multi-stage winding assembly was rotatable relative to a stationary magnetic assembly; however, it is believed that such past ECMs may have made many of the same requirements of the electronic circuitry therefor and that such electronic circuitry may have been equally applicable to such past ECMs. Further, while the more common past magnetic assembly for an ECM is believed to have been a permanent magnet assembly, another of such past magnetic assemblies has been an electro-magnet; however, it is believed that both of such past magnetic assemblies may have made many of the same requirements of the electronic circuitry for the ECM utilizing such past magnetic assemblies and that such electronic circuitry may have been equally applicable to the ECM utilizing either of such past magnetic assemblies.
With respect to the past higher power applications or heavy duty applications of past ECMs and the electronic circuitry therefor, as previously mentioned, such past ECM has been employed to drive apparatus having much greater torque and/or speed requirements, such as for instance a laundry machine or a blower fan for use in commercial or large scale air conditioning units or the like. In these past higher power applications, the switching transistors utilized in the power circuit for commutating the power supplied to the winding stages of the ECM were required to conduct exceedingly large currents in order to provide appropriate levels of power to the ECM to effect its operation in a suitable manner. In certain of these past higher power applications, by way of example a laundering application as disclosed in U.S. Pat. No. 4,556,827, the ECM was periodically called upon to provide relatively high torques. In the aforementioned laundering application, this high torque requirement occurred during the rotation reversals of ECM to effect agitation of the laundering basket during a wash mode operation. During a spin mode operation, the initial energization of the ECM may have required exceedingly large currents in order to initiate a spin rotation of the laundering basket and thereby effect centrifugal extraction of water from wet clothes contained in the laundering basket, but thereafter the ECM was capable of operating at relative higher speeds and lower currents. Depending upon the size of the laundering apparatus, it is believed that the ECM utilized to drive it may have been in the range of between about 1/4 to 1/2 horsepower, and in the past higher power application for driving a blower for an air conditioning unit, it is believed that the ECM utilized to drive it may have been in the range of between about 1/6 to 1/4 horsepower.
In the above discussed past higher power applications of the ECM and electronic circuitry therefor as well as other past higher power applications, the solid state switching devices in the power circuit for controlling the switched current between the winding stages of the ECM must be of a relatively large size in order to conduct the current magnitude associated with the higher horsepower ECM, and means must be provided for adequately dissipating the heat generated within such relatively large sized switching devices by virtue of such large currents passing therethrough. By way of contrast with the above discussed past lower power application utilizing lower power switching transistors, it is believed that the switching devices utilized in the past higher power applications must be capable of handling several orders of magnitude of current larger than that handled by such lower power switching transistors. Therefore, it is desirable not only to provide a means for dissipating the heat generated by the aforementioned higher power solid state switching devices but also to provide a means for positioning the power circuit, the regulating circuit and the control circuit at the ECM in order to avoid having multiple wiring connections running for relatively long distances between such circuits and the ECM.
In some higher power applications of the ECM and electronic circuitry therefor, it may also be desirable to incorporate the power circuit, the regulating circuit and the control circuit within a housing for the ECM; however, in this type of arrangement, it is believed that the heat generated by the solid state switching devices of the power circuit may be of such a magnitude as to endanger the solid state components of the regulating circuit and the control circuit unless the heat generated by such switching devices is adequately dissipated.